Thermotolerance of Isolated Mitochondria Associated with Heat Shock Proteins

Abstract

Mitochondria isolated from 2-day-old etiolated soybean (Glycine max) seedlings which had been subjected to various heat shock treatments, i.e. (A) 280C (2 h), (B) 380C (2 h), (C) 380C (2 h)-42.50C (0.5 h), and (D) 38°C (2 h)-42.50C (0.5 h)-280C (4 h), were monitored for 02 uptake using an oxygen electrode. Mitochondria isolated after all four heat shock treatments were active in 02 consumption at 280C in response to succinate and ADP (derived P/O ratios were 1.6, 1.7, 1.3, and 1.3, respectively.) The mitochondria from all four treatments were also active in 02 uptake at 42.50C. However, only mitochondria isolated after treatment (C) were tightly coupling at 42.50C (derived ADP/O ratio was about 1.4). Combined with our earlier findings on the subcellular localization of heat shock proteins, our present data demonstrate that association of heat shock proteins with mitochondria by treatment (C) enables them to phosphorylate at 42.50C (i.e. they become thermotolerant). Isolated mitochondria from treatment (C) and treatment (A) were compared by electron microscopy. They appeared to be very similar and no significant ultrastructural differences were noted.When soybean seedlings are shifted from a normal growth temperature of 28°C to 40°C HS,3 there is a dramatic change in protein synthesis and a new set of proteins known as HSPs are produced (1, 6, 7).There is a strong positive correlation between the accumulation of HSPs and the acquisition of thermotolerance (9-12, 14, 15, 19). The acquisition of thermotolerance appears to depend not only upon the synthesis of HSPs but also on their cellular localization (10, 24). In soybean seedlings, several HSPs become selectively localized in or associated with nuclei, mitochondria, ribosomes, and plasma membranes, as demonstrated by sucrose gradient centrifugation (10, 1 1). Specifically, the complex group of 15 to 18 kD HSPs was localized in these fractions during HS of soybean seedlings. The 70 kD HSP also exhibited similar localization, although to a lesser extent. In addition, some 22 and 24 kD HSPs were selectively localized in the mitochondrial fraction (10). This selective localization of HSPs was shown to be temperature dependent (10).The nature ofthe association ofthe HSPs with the organelle fraction of soybean is not known. We have tested whether the 'Supported by National Science Council of ROC under grant NSC76-0201-B002-1 1 to C. Y. Lin.

The plant sHSP superfamily: five new members in Arabidopsis thaliana with unexpected properties

“…The ER, P, M, and Po sHsps have all been localized in vivo to the respective organelles and cannot be detected in the cytoplasm. Mitochondrial sHsps are reported to be involved with the protection of mitochondrial proteins during hs and with increased thermotolerance (Chou et al 1989;Liu and Shono 1999;Sanmiya et al 2004). Similarly, overexpression of the chloroplast-localized sHsp protects photosystem II under some stress conditions (Neta-Sharir et al 2005;Guo et al 2007).…”

Characterization and Physiological Function of Class I Low-Molecular-Mass, Heat-Shock Protein Complex in Soybean

“…Some HSPs become selectively localized in cellular organelles in a temperature-dependent fashion and relocate to the cytoplasm after a 28°C incubation period (Lin et al, 1984). Isolated mitochondria with associated HSPs are functional in oxidative phosphorylation under thermal stress, suggesting that association of HSPs with organelles provide protection from heat damage (Chou et al, 1989 (Jinn et al, 1993). In soybean, depletion of the 15-to 18-kD HSPs in the HSP-enriched fraction resulted in the loss of the thermostabilizing ability, and this ability was again restored when these HSPs were added.…”

Heat shock proteins of barley mitochondria and chloroplasts Identification of organellar hsp 10 and 12: putative chaperonin 10 homologues

“…The novel 10 kDa hsp identified herein, fits these criteria and may therefore represent plant mitochondrial opal0. The identity of the 24 kDa stress protein heat induced in these studies is not known but, mitoehondrial 22 kDa and 24 kDa hsps have been observed in soybean [33]. Analysis of chloroplast proteins revealed the presence of heat shock inducible proteins with apparent MWs of 75, 72, 60, 18 and 12 kDa, respectively.…”